diff --git a/README.md b/README.md
index 5da60e2..98418ed 100644
--- a/README.md
+++ b/README.md
@@ -376,7 +376,7 @@ Section creation order:
 1. ✅ `shellIndex`, `shellBlob`. No dependencies.
 1. ✅ userGids. No dependencies.
 1. ✅ Users. Requires `userGids` and shell.
-1. Groupmembers. Requires Users.
+1. ✅ Groupmembers. Requires Users.
 1. Groups. Requires Groupmembers.
 1. `idx_*`. Requires offsets to Groups and Users.
 1. Header.
diff --git a/src/group.zig b/src/group.zig
index 1f854e8..1377b33 100644
--- a/src/group.zig
+++ b/src/group.zig
@@ -31,14 +31,14 @@ pub const Group = struct {
     }
 };
 
-const GroupStored = struct {
+pub const GroupStored = struct {
     gid: u32,
     name: []const u8,
     members_offset: u64,
 };
 
-const PackedGroup = struct {
-    const alignment_bits = 3;
+pub const PackedGroup = struct {
+    pub const alignment_bits = 3;
 
     const Inner = packed struct {
         gid: u32,
@@ -119,6 +119,7 @@ const PackedGroup = struct {
         arr: *ArrayList(u8),
         group: GroupStored,
     ) packErr!void {
+        std.debug.assert(arr.items.len & 7 == 0);
         const groupname_len = try validate.downCast(u5, group.name.len - 1);
         try validate.utf8(group.name);
         const inner = Inner{
@@ -129,7 +130,6 @@ const PackedGroup = struct {
         try arr.*.appendSlice(mem.asBytes(&inner));
         try arr.*.appendSlice(group.name);
         try compress.appendUvarint(arr, group.members_offset);
-        try pad.arrayList(arr, alignment_bits);
     }
 };
 
@@ -142,9 +142,8 @@ pub fn someMembers(
 ) Allocator.Error!BufSet {
     var bufset = BufSet.init(allocator);
     errdefer bufset.deinit();
-    for (members) |member| {
+    for (members) |member|
         try bufset.insert(member);
-    }
     return bufset;
 }
 
@@ -171,6 +170,7 @@ test "construct PackedGroups" {
 
     for (groups) |group| {
         try PackedGroup.packTo(&buf, group);
+        try pad.arrayList(&buf, PackedGroup.alignment_bits);
     }
 
     var i: u29 = 0;
diff --git a/src/sections.zig b/src/sections.zig
index dd02817..ad46184 100644
--- a/src/sections.zig
+++ b/src/sections.zig
@@ -243,7 +243,7 @@ pub fn usersSection(
 ) error{ OutOfMemory, Overflow, InvalidRecord }!UsersSection {
     var idx2offset = try allocator.alloc(u32, corpus.users.len);
     errdefer allocator.free(idx2offset);
-    // as of writing each user takes 15 bytes + strings + padding, padded to
+    // as of writing each user takes 12 bytes + blobs + padding, padded to
     // 8 bytes. 24 is an optimistic lower bound for an average record size.
     var blob = try ArrayList(u8).initCapacity(allocator, 24 * corpus.users.len);
     errdefer blob.deinit();
@@ -257,6 +257,7 @@ pub fn usersSection(
             gids.idx2offset[i],
             shells.indices,
         );
+        try pad.arrayList(&blob, userImport.PackedUserHash.alignment_bits);
     }
     return UsersSection{
         .idx2offset = idx2offset,
@@ -317,6 +318,48 @@ pub fn groupMembers(
     };
 }
 
+pub const GroupsSection = struct {
+    // group index -> offset in blob
+    idx2offset: []const u32,
+    blob: []const u8,
+
+    pub fn deinit(self: *GroupsSection, allocator: Allocator) void {
+        allocator.free(self.idx2offset);
+        allocator.free(self.blob);
+        self.* = undefined;
+    }
+};
+
+pub fn groupsSection(
+    allocator: Allocator,
+    corpus: *const Corpus,
+    members_offset: []const u64,
+) error{ OutOfMemory, Overflow, InvalidRecord }!GroupsSection {
+    var idx2offset = try allocator.alloc(u32, corpus.groups.len);
+    errdefer allocator.free(idx2offset);
+
+    var blob = try ArrayList(u8).initCapacity(allocator, 8 * corpus.groups.len);
+    errdefer blob.deinit();
+
+    for (corpus.groups) |group, i| {
+        const group_offset = try math.cast(u32, blob.items.len);
+        std.debug.assert(group_offset & 7 == 0);
+        idx2offset[i] = group_offset;
+        const group_stored = groupImport.GroupStored{
+            .gid = group.gid,
+            .name = group.name,
+            .members_offset = members_offset[i],
+        };
+        try groupImport.PackedGroup.packTo(&blob, group_stored);
+        try pad.arrayList(&blob, groupImport.PackedGroup.alignment_bits);
+    }
+
+    return GroupsSection{
+        .idx2offset = idx2offset,
+        .blob = blob.toOwnedSlice(),
+    };
+}
+
 // cmpUser compares two users for sorting. By username's utf8 codepoints, ascending.
 fn cmpUser(_: void, a: User, b: User) bool {
     var utf8_a = (unicode.Utf8View.init(a.name) catch unreachable).iterator();
@@ -352,6 +395,7 @@ pub const AllSections = struct {
     shell_blob: []const u8,
     user_gids: UserGids,
     group_members: GroupMembers,
+    groups: GroupsSection,
 
     pub fn init(
         allocator: Allocator,
@@ -376,6 +420,11 @@ pub const AllSections = struct {
             corpus,
             users.idx2offset,
         );
+        const groups = try groupsSection(
+            allocator,
+            corpus,
+            group_members.idx2offset,
+        );
         return AllSections{
             .allocator = allocator,
             .bdz_gid = bdz_gid,
@@ -388,6 +437,7 @@ pub const AllSections = struct {
             .user_gids = user_gids,
             .users = users,
             .group_members = group_members,
+            .groups = groups,
         };
     }
 
@@ -400,6 +450,7 @@ pub const AllSections = struct {
         self.user_gids.deinit(self.allocator);
         self.users.deinit(self.allocator);
         self.group_members.deinit(self.allocator);
+        self.groups.deinit(self.allocator);
         self.* = undefined;
     }
 };
@@ -510,7 +561,7 @@ test "test corpus" {
     try testing.expectEqual(groupsOfVidmantas[2], g_all);
 }
 
-test "test group members" {
+test "test groups and group members" {
     const allocator = testing.allocator;
     var corpus = try testCorpus(allocator);
     defer corpus.deinit();
@@ -529,7 +580,11 @@ test "test group members" {
             const want_user_offset = sections.users.idx2offset[user_idx];
             try testing.expectEqual(got_user_offset, want_user_offset);
         }
+        try testing.expectEqual(it.next(), null);
     }
+
+    //var it = userImport.PackedUserHash.iterator(sections.groups.blob);
+    //_ = it;
 }
 
 test "userGids" {
@@ -555,6 +610,7 @@ test "userGids" {
         while (try it.next()) |gid| : (i += 1) {
             try testing.expectEqual(gid, corpus.groups[groups[i]].gid);
         }
+        try testing.expectEqual(i, groups.len);
     }
 }
 
diff --git a/src/user.zig b/src/user.zig
index f94370e..91a5a1f 100644
--- a/src/user.zig
+++ b/src/user.zig
@@ -84,7 +84,7 @@ fn packedUser(comptime ShellIndexType: type) type {
     return struct {
         const Self = @This();
 
-        const alignmentBits = 3;
+        pub const alignment_bits = 3;
 
         const Inner = packed struct {
             uid: u32,
@@ -165,7 +165,7 @@ fn packedUser(comptime ShellIndexType: type) type {
             const gids_offset = try compress.uvarint(bytes[end_strings..]);
             const end_blob = end_strings + gids_offset.bytes_read;
 
-            const nextStart = pad.roundUp(usize, alignmentBits, end_blob);
+            const nextStart = pad.roundUp(usize, alignment_bits, end_blob);
             var next: ?[]const u8 = null;
             if (nextStart < bytes.len)
                 next = bytes[nextStart..];
@@ -207,6 +207,7 @@ fn packedUser(comptime ShellIndexType: type) type {
             additional_gids_offset: u64,
             idxFn: ShellIndexType,
         ) error{ InvalidRecord, OutOfMemory }!void {
+            std.debug.assert(arr.items.len & 7 == 0);
             // function arguments are consts. We need to mutate the underlying
             // slice, so passing it via pointer instead.
             const home_len = try validate.downCast(u6, user.home.len - 1);
@@ -231,8 +232,6 @@ fn packedUser(comptime ShellIndexType: type) type {
             };
             const innerBytes = mem.asBytes(&inner);
 
-            // innerBytes.len is longer than @sizeOf(Inner). We want to copy
-            // only the @sizeOf(Inner)-number of bytes.
             try arr.*.appendSlice(innerBytes[0..@sizeOf(Inner)]);
             try arr.*.appendSlice(user.home);
 
@@ -242,20 +241,6 @@ fn packedUser(comptime ShellIndexType: type) type {
             if (inner.shell_here)
                 try arr.*.appendSlice(user.shell);
             try compress.appendUvarint(arr, additional_gids_offset);
-            try pad.arrayList(arr, alignmentBits);
-        }
-
-        // maxSize is the maximum number of records a PackedUser can take
-        // (struct + strings).
-        pub fn maxSize() usize {
-            comptime {
-                const unpadded = @sizeOf(Inner) +
-                    math.maxInt(u6) + 1 + // home
-                    math.maxInt(u5) + 1 + // name
-                    math.maxInt(u6) + 1 + // shell
-                    math.maxInt(u8); // gecos
-                return pad.roundUp(u64, alignmentBits, unpadded);
-            }
         }
 
         pub fn uid(self: Self) u32 {
@@ -360,8 +345,10 @@ test "construct PackedUser section" {
         .home = "/",
         .shell = "/",
     } };
-    for (users) |user|
+    for (users) |user| {
         try PackedUserTest.packTo(&buf, user, math.maxInt(u64), TestShellIndex{});
+        try pad.arrayList(&buf, PackedUserHash.alignment_bits);
+    }
 
     var i: u29 = 0;
     var it1 = PackedUserTest.iterator(buf.items, testShell);
@@ -380,27 +367,6 @@ test "construct PackedUser section" {
     try testing.expectEqual(users.len, i);
 }
 
-test "PackedUser.maxSize()" {
-    // TODO(motiejus) try using a slice that points to an array in stack.
-    // As of writing, I am getting a stack smashing error.
-    var buf = try ArrayList(u8).initCapacity(
-        testing.allocator,
-        PackedUserHash.maxSize(),
-    );
-    defer buf.deinit();
-
-    const largeUser = User{
-        .uid = math.maxInt(u32),
-        .gid = math.maxInt(u32),
-        .name = "Name" ** 8, // 32
-        .gecos = "Gecos" ** 51, // 255
-        .home = "Home" ** 16, // 64
-        .shell = "She.LllL" ** 8, // 64
-    };
-    try PackedUserTest.packTo(&buf, largeUser, math.maxInt(u29), TestShellIndex{});
-    try testing.expectEqual(PackedUserTest.maxSize(), buf.items.len);
-}
-
 test "User.clone" {
     var allocator = testing.allocator;
     const user = User{